The present inventors previously succeeded in isolating a naturally occurring human MACIF, a so-far unknown protein regulating the complement system, in pure form from the human normal erythrocyte membrane (Japanese Patent Application No. 63-310642). They found that the human MACIF inhibits the activation of the late complement components or, in other words, inhibits hemolysis resulting from human MAC formation and, in this respect, the human MACIF is distinguished from and superior to the known complement-regulating substances that inhibit the activation of the early complement components, and that the naturally occurring human MACIF has the following N-terminal amino acid sequence: ##STR1## Furthermore, they found that this naturally occurring human MACIF is a glycoprotein having a molecular weight of 18,000.+-.1,000 (as determined by SDS-polyacrylamide gel electrophoresis) with a phosphatidylinositol anchor (hereinafter abbreviated as "PI-anchor") at the C terminus.
For further studying of the above-mentioned protein having human MACIF activity and for developing the practical use of the protein as a drug, it is essential to obtain the protein in a pure and homogeneous form, and in sufficiently large quantities. For this purpose, application of the recombinant DNA technology appears to be the most effective means. However, the gene required for the means has not been isolated as yet.
Accordingly, an object of the invention is to provide a gene coding for a protein having human MACIF activity.
Another object of the invention is to provide a replicable expression vector capable of expressing the gene coding for a protein having human MACIF activity.
A further object of the invention is to provide a microorganism or cells transformed with the expression vector.
A still further object is to provide a genetically engineered protein having human MACIF activity.